Primary amino groups number among the most accessible of heterocyclic substituents, but they are of little utility in further synthetic transformations. This proposal suggests a number of novel strategies for (a) the conversion of primary amino substituents into nitroso groups which, as superb dienophiles and extremely reactive electrophiles, are versatile intermediates for the elaboration of functionalized alkyl amino groups, including sugar derivatives, and for the construction of both fused and pendent heterocyclic systems; (b) the in situ conversion of primary amino groups to nitro groups (by oxidation of the above nitroso compounds) which can then be readily displaced by nucleophiles; the amino-to-nitro conversion would also represent an Umpolung of the starting primary amino group; and (c) the conversion of primary (heterocyclic) amino substituents into sulfilimines and phosphinimes as intermediates for further amino group functionalizations. Of particular significance would be the conversion of these ylides to non-protonated diazonium salts which should undergo the entire spectrum of diazonium coupling and replacement reactions characteristic of normal aryldiazonium salts. These transformations would represent a significant advance in synthetic methodology in heterocyclic chemistry.